Speaker
Description
Airborne experiment on SAR based observation of snow mass in Alpine terrain
Helmut Rott, Thomas Nagler, Stefan Scheiblauer, Ralf Horn, Jens Fischer, Matteo Pardini, Julia Kubanek
Abstract
In March 2021 a field experiment was conducted in the high Alpine test site Woergetal in the Austrian Alps, exploring the application potential and performance of snow mass (snow water equivalent, SWE) retrieval by C-and L-band SAR sensors. Multiple repeat-pass acquisitions were acquired on seven days with the airborne F-SAR of DLR, operating in dual frequency, C-band and L-band, polarimetric mode. The SAR data cover periods without snowfall and span also two snowfall events with mean accumulation (delta-SWE) amounts of 13 mm, respectively 65 mm. Snow depth transects and snow pit measurements were made at three comparatively level sections of the test site in different elevations. Main motivation for the experiment was the development and evaluation of concepts and tools for the utilization of the repeat-pass InSAR technique for snow mass monitoring, assessing the potential of future missions such as the Radar Observation System for Europe at L-band (ROSE-L), Sentinel-1 Next Generation (NG) and the geosynchronous C-band SAR mission Hydroterra that had been proposed in response to the ESA Call for Earth Explorer 10 Mission Ideas. Besides focussing on the use of repeat-pass interferometry for SWE retrieval, we also checked the information content of polarimetric parameters in respect to changes in snow mass. Among these, the C-band HH-VV co-polarized phase difference shows a distinct response to the accumulation of fresh snow, the spatial pattern of which, however, does not exactly reflect the observed snow depth.
For the repeat-pass InSAR based SWE retrievals of the two snowfall events three approaches were implemented and evaluated using the following configurations: (i) C- and L-band repeat-pass data in full spatial resolution applying the conventional repeat-pass InSAR technique; (ii) simulated C-band repeat-pass data reflecting the spatial resolution and sampling of the Hydroterra system; (iii) C- and L-band repeat-pass data in full spatial resolution applying split-bandwidth processing to obtain two sub-band SLC images that are used to generate differential split-bandwidth (Delta-k) interferograms for each date. These interferograms are used for repeat-pass DInSAR processing. In each of these configurations the phase of corner reflectors, cleaned of snow, was used in the differential interferograms as reference for zero delta-SWE. With the Delta-k method the problem of 2-pi phase ambiguity due to intense snowfall events or long time spans can be overcome, though the sensitivity in respect to SWE is reduced. Examples of phase, coherence and SWE products, obtained by the three approaches, will be presented, the performance of the products will be compared, and the use and complementary for obtaining continuous SWE time series will be discussed.
